The goal of the proposed work is to understand cellular and environmental factors that regulate neural crest development. Along with this, we will study morphologic and biochemical changes that accompany differentiation the study focuses on de novo expression in vitro of adrenergic cells, one of the neural crest derivatives. The continuation of this work extends our finding that de novo differentiation of crest cells into adrenergic elements occurs in vitro, in the absence of non-crest interactions. This makes possible studies of cellular and molecular changes that take place prior to acquisition of formaldehyde induced fluorescence. These studies are planned to further characterize the in vitro conditions that promote adrenergic differentiation. We will examine changes in our in vitro methods that promote clonal expression of adrenergic neuroblasts. In addition we are studying the onset of enzyme synthesis involved in the production of noradrenaline. Studies are also underway for defining the developmental potential of early neural crest cells. Such studies will provide insight into the factors regulating divergence in this important embryonic system.